This application claims the priority of Korean Patent Application No. 10-2004-0014245, filed on Mar. 3, 2004, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an optical detection system, and more particularly, to an optical detection device that biochemically analyzes samples of microfluidic chips such as DNA chips or protein chips.
2. Description of the Related Art
In biological diagnosis, it has recently become necessary to detect biological molecules contained in very low concentrations in samples having a very small volume. Consequently, efforts are underway to develop a highly sensitive sensor.
For biochemical applications, an optical sensor is usually preferable because it is both chemically stable and easily machined. One type of sensor suitable for biochemical application is based on a structure of illumination excitation. This sensor combines biochemical selectivity caused by recognition of molecules to be analyzed with spatial selectivity caused by evanescent field excitation.
FIG. 1 is a schematic diagram of a conventional optical detection device 10 suitable for biochemical applications.
Referring to FIG. 1, the optical detection device 10 includes an optical waveguide 11, a glass substrate 12, a first diffraction grating 13, a second diffraction grating 14, a HeNe laser 15, a lens 16, a Dammann diffraction grating 17, an achromatic cylindrical lens 18, and a mirror 19.
The optical waveguide 11, formed on the glass substrate 12, is made from a material such as tantalum pentoxide (TaO5), and is used as a transducer for a biochemical sensor. Also, the first and second diffraction gratings 13 and 14 are patterned in the glass substrate 12 through a photolithographic process to have identical structures with the same depth and pitch, and a patterned shape is transferred to the optical waveguide 11 deposited on the first and second diffraction gratings 13 and 14.
The first diffraction grating 13 is adapted to facilitate transmission of excitation light into the optical waveguide 11, while the second diffraction grating 14 is adapted to transfer the excitation light from the optical waveguide 11 to the optical detection device.
Referring to FIG. 1, the excitation light radiated from the HeNe laser 15 is reflected by the mirror 19 and incident on the lens 16. The excitation light incident on the lens 16 is spread to have a desired spot size and then is incident on the Dammann diffraction grating 17. The Dammann diffraction grating 17 divides the incident excitation light into 16 parts by minimizing an intensity of the excitation light at angles corresponding to even numbers of degrees and maximizing the intensity at angles corresponding to odd numbers of degrees.
Next, the excitation light which has been divided into 16 parts passes through the achromatic cylindrical lens 18 and is transduced into an excitation beam having 16 parallel components. Here, the Dammann diffraction grating 17 is positioned at a focus of the achromatic cylindrical lens 18, such that the excitation beam passing through the achromatic cylindrical lens 18 is aligned in parallel.
FIG. 2A is a diagram showing propagation of the excitation light through the achromatic cylindrical lens 18. FIG. 2B is a graph showing an intensity profile of the excitation light having passed through the achromatic cylindrical lens 18. FIG. 2C is a photograph of excitation light having passed through the achromatic cylindrical lens 18.
Referring again to FIG. 1, the excitation beam having 16 parallel components enters the optical waveguide 11 via the first diffraction grating 13 and propagates through the optical waveguide 11. Here, if a sample, for example, a microfluidic chip, is located on the optical waveguide 11, the excitation beam passing through the optical waveguide 11 excites the sample which then radiates light. Light radiating from the exited sample is added to the light propagating through the optical waveguide 11, and the combined light is incident on 16 microlenses via the second diffraction grating 14.
The 16 microlenses focus the incident light on the optical detection device, which comprises 16 photomulitpliers (PMTs). Also, in order to reduce interference between the beams of light incident on the 16 PMTs, the optical detection device may include a filter having 16 orifices.
The conventional optical detection device has the disadvantages of it being difficult to align the 16-part excitation beam with the 16 microlenses and to align the 16 microlenses with the 16 PMTs of the optical detector.
Also, the conventional optical detection device employs the achromatic cylindrical lens 18 to create parallel beams of light. Therefore, there is a drawback in that since the achromatic cylindrical lens 18 has a Gaussian distribution, as shown in FIGS. 2A to 2C, the intensity of the excitation light is not spatially uniform.